Cone Nebula. Optical image of the dark Cone Nebula taken by the new Hubble Space Telescope Advanced Camera for Surveys (ACS) on April 2nd 2002. The Cone Nebula is a dense, dark pillar of gas and dust seen silhouetted against part of the bright red emission nebula NGC 2264. The tip of the pillar is illuminated by hot young stars (out of frame at top). Radiation from these stars heats the cool gas of the nebula, releasing it into surrounding space. There it is ionised by ultraviolet light, causing it to glow red. The Cone Nebula lies around 2500 light years from Earth in the constellation Monoceros.